A known shear punching die assembly includes a lower die unit that has a main punch and a stripper disposed around the main punch, and an upper die unit that has an ejector positioned axially opposite to the main punch and a die disposed around the ejector. In the known art, a material (a sheet material) is transferred and placed between upper and lower die units of the shear punching die assembly. Thereafter, the upper and lower die units are closed (i.e., a die closing operation is performed), so that the main punch of the lower die unit engages the die of the upper die unit. As a result, the material is punched out by the main punch, so that a formed article or work is formed. At this time, the ejector is moved to a retracted position with the work, so that the work can be retained in the die. Subsequently, the upper and lower die units are opened (i.e., a die opening operation is performed). Thereafter, a hydraulic removing mechanism (a hydraulic cylinder) connected to the ejector is actuated so as to push the ejector. As a result, the work retained in the die is ejected or removed from the die. Thus, a punching operation (a work manufacturing operation) is completed. Further, such a known shear punching die assembly is taught, for example, by Japanese Laid-open Patent Publication Number 6-31695.
However, in the known shear punching die assembly, it is not possible to rapidly eject the work from the die of the upper die unit, because the hydraulic removing mechanism cannot generally be moved at high speeds. That is, a work removing operation cannot be speeded up beyond a certain level. Therefore, even if a punching operation of the material is speeded up, a manufacturing speed of the work cannot substantially be increased. This may lead to a speed up limitation of a manufacturing speed of the work.
In another shear punching die assemblies, a motor driven removing mechanism or a spring driven removing mechanism is used in place of the hydraulic removing mechanism. Because the motor driven removing mechanism or the spring driven removing mechanism can generally be moved at high speeds than the hydraulic removing mechanism, the work removing operation can be speeded up. However, these shear punching die assemblies have some drawbacks. For example, in the spring driven removing mechanism, the ejector is normally biased toward the main punch. Therefore, the work can be thrust back from the die of the upper die unit toward a processed material before the upper and lower die units are sufficiently opened. As a result, the work may be pushed toward the processed material at the start of the die opening operation. The pushed work may possibly reengage a punched hole of the processed material. Therefore, extra time is required for removing the work from the processed material. Thus, these shear punching die assemblies still admit of improvement.